"I… am invincible?"
Natsuro felt the depth of his current strength. Then, glancing at Kaguya, who was still collapsed and unable to rise, he slowly walked toward her.
"Why… can you use the powers of the Rinnegan?" Kaguya asked, her voice tinged with both disbelief and despair.
"Because… when you become strong enough, every ability has its rules, and I simply grasped those rules and used them," Natsuro replied calmly.
Kaguya was stunned into silence. What he said sounded so simple, but who could actually achieve such a thing?
This might seem similar to how the Sharingan copies jutsu, but in reality, there was a fundamental difference. The Sharingan merely reproduces the chakra flow and hand seals to mimic a technique.
But what he spoke of was true mastery, understanding the essence of the ability itself. He didn't need to copy it. He could even use an entirely different method, and still produce the same effect.
For instance, even the highest-tier Mangekyō Sharingan couldn't replicate Rinnegan techniques. But Natsuro could observe, comprehend the operational principles, and then simply… use them.
Seeing that Kaguya was still confused, Natsuro took his time and began to explain.
"Kaguya, you know about the Sage Arts your son Hagoromo, the Sage of Six Paths, once learned, don't you?" he asked.
Kaguya nodded, still puzzled. What does Sage Mode have to do with the Rinnegan? Could it really be that powerful?
Natsuro nodded as if reading her mind, grateful he didn't need to explain what Sage Mode and Sage Arts were from the ground up.
"The Sage Mode of the Sage of Six Paths was a fusion of his Ōtsutsuki chakra and natural energy. It didn't grant particularly unique powers. But because the chakra quality of the Ōtsutsuki clan is so overwhelmingly high, his Sage Mode ended up far stronger than expected," Natsuro explained.
"…And what does that have to do with you using Shinra Tensei?" Kaguya still didn't understand.
"Patience. In truth, Sage Modes usually come with special enhancements tied to specific species traits. For example, Kaguya, have you heard of a creature called the leafcutter ant?" Natsuro asked.
Before Kaguya could respond, Natsuro shook his head with a faint smile. "Forget it. I doubt you even understand human abilities, let alone know about ants."
Then he continued, "This is an ant capable of lifting over 50 times its own weight."
"So what?" Kaguya frowned. "Even if an ant lifts 50 times its own weight, that's still barely the weight of a leaf."
"What if I told you," Natsuro said, "that I based a Sage Mode on that ant's traits? Oh, and by the way, the 50x lifting capacity I mentioned doesn't involve any chakra or natural energy. That's its base strength."
At that, Kaguya's pupils shrank. She was starting to understand, this meant that upon entering such a Sage Mode, one's base strength would increase by multiple factors… and once chakra or natural energy were added…
The multiplication could be astronomical.
"And by the way," Natsuro added, "leafcutter ants aren't even the strongest in terms of relative strength. There are creatures that can lift nearly a thousand times their own weight without chakra or nature energy. It's insane."
Kaguya fell into silence, clearly beginning to comprehend.
"So, you're saying… there's a kind of special Sage Mode that lets you instantly master certain abilities?" she asked.
Natsuro nodded and smiled. "Now, do you know what separates humans and animals before either learn to use chakra or natural energy?"
Kaguya didn't answer. She was thinking.
But Natsuro didn't wait. "Intelligence—or to be precise, thought."
Kaguya's expression shifted as she began to understand something deeper, staring at Natsuro.
"Humans aren't strong in terms of individual physical prowess in nature. But they became the dominant species because of their intelligence. They used that intelligence to create tools, and after discovering chakra, they created all kinds of ninjutsu," Natsuro said, glancing at her again with a soft smile.
"And by the way, those techniques that gave you such a hard time, like the Eight Gates Formation and Flying Thunder God, they weren't even invented by me."
Kaguya was silent. She couldn't help but wonder: If I had learned those techniques… if I had learned how to fight properly… would things have ended differently?
But as she looked at Natsuro, she sighed inwardly. Somehow… with him around, it still felt impossible.
"So, the ability to see through everything, that is the Human Sage Art. It may not give strength like the ant's Sage Mode, or speed like the cheetah's, but it gives the user the ability to comprehend all things… and to create anything," Natsuro said, a bit awed himself.
"That's how I remembered Shinra Tensei, studied it, and then simply used it. That's all there is to it."
Natsuro sighed in admiration. The Human Sage Art truly was the most fitting path for humanity from the very beginning.
After learning about all the various Sage Modes in existence, he had always wondered, if every creature had a corresponding Sage Mode that amplified their natural gifts, didn't humans also have their own?
And now, as his life had neared its end, Natsuro had finally grasped it: the Human Sage Art.
Unfortunately, there was one paradox...
To master the Human Sage Art, one had to understand the essence of all things. But understanding that essence was nearly impossible. Even Natsuro had only achieved it through his method of fusing all Sage Modes together.
Which meant… directly teaching others the Human Sage Art would be nearly impossible too.
He thought for a moment, then smiled. Maybe he was overthinking it.
Perhaps the Human Sage Art wasn't that hard to access. Maybe the earliest form of it lacked the deep comprehension of the source that he had now. But…
It had one innate strength, the power to learn.
And so, Natsuro realized, the path he should have followed from the very start was the Human Sage Art. Using its learning ability, he could have gradually expanded his knowledge and understanding of all things, eventually reaching the source he now stood at.
And then… perhaps even stepped into the domain of the Primal Sage?
Maybe.
Natsuro couldn't say for certain. He hadn't walked that path, so even if it seemed possible, he couldn't confirm it.
Still, it might be the most natural and correct path of all. If he had mastered the Human Sage Art as a child, his journey might have gone much more smoothly.
Too bad… there was no one back then who could've taught young Natsuro the Human Sage Art.
"I see…" Kaguya's pale eyes glimmered with realization, though her gaze was also lost, uncertain.
She seemed to have understood something, yet felt even more directionless than before.
Perhaps it was already too late. From the moment she devoured the God Tree's fruit, no one had ever dared to be her teacher. No one had ever tried to guide her.
Perhaps that was the true reason she had been sealed by her sons, and now, after her hard-fought "resurrection," was about to be sealed again.
"Natsuro Shindōkawa… you're going to seal me now, aren't you?" Kaguya asked, no longer resisting. She had once thought about struggling… but after this conversation, she realized she likely stood no chance at all.
He had seen through all of her abilities. Which meant…
Natsuro could use everything Kaguya could, All-Killing Ash Bones, Amenominaka… everything. In that case, how could she possibly win?
"You've given up?" Natsuro looked at her and sighed. He had actually wanted to fight her again once she had fully recovered, to test his new self—but alas, she gave up after their chat.
Still, it couldn't be helped. As she thought, he could now use all her powers. In fact, any technique he had seen before, he could now reproduce. Whether it was Kekkei Genkai or even Kekkei Tōta.
He had already figured it out, being able to use Kekkei Mōra didn't mean you could automatically use Kekkei Genkai, but those who could wield Kekkei Mōra could easily deduce and reproduce any Kekkei Genkai if they tried.
Why? Because the chakra proportions needed for fusion were different.
The mix required to create Kekkei Mōra with seven chakra types differed from the precise ratios needed for each specific Kekkei Genkai or Kekkei Tōta.
Which meant that, in theory, the types of Kekkei Genkai were not limited to just combinations of two elements, different chakra ratios could potentially produce entirely new results.
However, he didn't yet have the time to sort through everything he had seen. Once he finished what needed to be done, he planned to return to his original starting point, and from there, refine everything he now possessed to its absolute perfection.
For example, he could try to develop Kekkei Tōta beyond Dust Release, or even experiment with combining four or five chakra natures to unlock entirely new powers…
One thing was certain, though... Natsuro was about to return to that familiar, boring state of having no rivals.
There was one difference from before, back then, he could at least look forward to the various Six Paths-level opponents in the Fourth Great Ninja War.
And as it turned out, he was right. This war had kept him fighting from the very beginning all the way to the end, battling the Kage of each village, then Edo Madara, Six Paths Obito, Six Paths Madara, and finally… Kaguya Ōtsutsuki herself.
Even for him, the experience had been thoroughly exhilarating.
But when he thought about the road ahead, a strange emptiness crept in. There was nothing left to look forward to anymore.
The other Ōtsutsuki clan members, perhaps?
Natsuro didn't believe they'd surpass Six Paths Madara in strength. Maybe a few of them might, but… would that be enough to reach his current level?
So the future, most likely… would be a bit dull.
Still, he wanted to become even stronger. Even if he couldn't currently see any path forward, he wouldn't give up.
Does one need a reason to grow stronger? Natsuro didn't think so. The pursuit of strength is a reason in itself.
He slowly approached Kaguya, then placed his hand on her abdomen, right before her eyes.
In the next moment, both Natsuro and Kaguya vanished, reappearing once more in the world of the shinobi. What Natsuro was about to do now had to do with this world.
Then, an endless flow of chakra began to surge from Kaguya's belly and into Natsuro's body.
"That's… that's mine…" Kaguya's eyes turned red in an instant. She looked like a child being robbed of her most precious toy, she wanted to resist, but…
In the end, she looked at Natsuro and let out a long, helpless sigh.
A child cannot win against an adult.
Natsuro ignored her and continued to absorb her chakra. At this moment, Kaguya possessed nearly all the chakra in the world.
Even if a tiny portion was missing, whether it was 100% or 99.99%, it didn't matter.
The vast, immeasurable chakra flowed into Natsuro like a whale gulping water.
Even so, absorbing an entire world's worth of chakra was no easy feat, Natsuro still needed considerable time to take it all in.
After what seemed like a long while, he finally finished. Every drop of chakra within Kaguya had been drawn into his body. The blood-red Rinnegan on her forehead had now closed, she could no longer open that eye.
Kaguya's consciousness slowly faded. Her body shriveled, the result of having lost all chakra, after all, chakra also contains vital physical energy.
Now, feeling the immense amount of chakra stored inside himself, Natsuro couldn't help but murmur:
"No wonder Madara exploded. How could a single person possibly contain the chakra of an entire world?"
He didn't include himself in that statement, because he had already stepped into the final domain. While he was indeed full, he wasn't overloaded.
If he had to absorb another world's worth of chakra, then it might overwhelm him, but even then, he would be in better shape than Madara, since he had the ability to rapidly expend excess chakra.
Now, Natsuro took a deep breath. A serious glint appeared in his eyes.
At last, it was time to do what he had always intended:
Convert all of this chakra into natural energy, and return it to the world.
To restore this world… to its original state.